Bucket attachment for turbine wheels



3952 G. A. STURGESS 2,605,996

BUCKET ATTACHMENT FOR TURBINE WHEELS Filed Oct. 20, 1949 Inventor: Geor e A. Stur-jge $5,

HIS Attorney.

Patented Aug. 5, 1952 BUCKET A'rmAcnMENfr-Fon' WHEELS George A. Sturges'a'Espei-ance, 1N; g assignor to General Electric Company, a corporation of New York Emmi with sie i i ief etiszs 1. This invention relates to turbo-machine rotor structure and, in particular, to a structure for attaching blades or buckets to the periphery of an axial flow turbo-machine wheel.

Conventional turbine buckets usually comprise a blade portion, a base portion .and a securing portion. The securing portion frequently resembles a V having serrated sides arranged to match a V-groove in the turbine wheel; the groove, in turn, having corresponding serrated edges. Sometimes the securing portion of the bucket is inserted axially into axial grooves on the wheel, while more frequently the wheel is provided with a V-groove around its periphery and buckets are inserted in one or more slots in the periphery and slid along the groove one after the other until buckets substantially surround the wheel.

The conventional arrangements mentioned above have not produced the desired result in 1 Claim. (01. 253 17 I gas turbine work. Failures have occurred in the buckets, usually in the securing portion at the first row of serrations below the base portion. These fatigue failures have been attributed to poor vibration resistance in the buckets.

It is an object of this invention to provide an improved arrangement for mounting buckets or blades on a turbo-machine rotor.

It is a further object of this invention to provide a mounting for a bucket on a turbine wheel wherein the bucket has a natural frequency sufllciently different from the conventional bucket to minimize vibration problems.

These, and other objects and advantages of this invention, will become apparent and the invention will be better understood from the following description referring to the accompanying drawing, and the features of novelty which characterize this invention will be pointed out with particularity in the claim annexed to and forming a part of this specification.

Broadly, this invention comprises an improved structure for installing buckets on a turbine wheel. The bucket has, instead of the usual V- type dovetail construction, an inverted V-shaped groove with axially extending serrated sides that provide two legs on which the bucket stands when secured to a turbine wheel.

The single figure of the drawing is a front elevation of a section of a turbine wheel with buckets mounted thereon in accordance with the invention.

Referring to the drawing, a turbine wheel I is provided with evenly spaced axially extending V-shaped grooves 2 having serrations 3 extendn al neth i esf *v. h o t ed stortio'n left on the periphery of the wheel between adSacent grooves fare known as lands. V

A plura l'ity of buckets fly'h'a'ving blades 5 of a conventional form, arejrnounted on turbine wheel 1. Each bucket also has afbase s'ectionjliv which is both the securing "portion of the bucke'tand the support for the bucket 'blafde. .B'ase sections or portions tare "of" a width equal "to the distance between radialjlirres passing'thjrou'ghthe centers of any two consecutive V-grooves in the turbine wheel, and areof a depth substantially equalfto that of the V-shaped grooves in the turbine wheel. The height of the base section 6 is slightly greater than the depth of the grooves in the turbine wheel. Centrally on each base section an inverted V-shaped groove I is cut to provide legs 8 having serrations 8a that match the serrations 3 in the V-grooves on the turbine wheel.

When a turbine bucket 4 is mounted on turbine wheel I, groove 1 in the bucket is axially inserted over a land 9 between two of the V- grooves on the turbine wheel. Serrations 8a in the bucket operatively engage serrations 3 in the turbine wheel, preventing radial movement of the bucket away from the wheel.

Each bucket base 6 is further provided with a lip and shoulder arrangement. That is, one side ll of the bucket base is provided along its full depth with a lip portion ID that extends outwardly from the side. The opposite side of base 6 has a chamfered shoulder l2 which matches lip ID in dimensions. Successive lips rest on successive shoulders. Such a lip and shoulder arrangement is a convenient structure for strengthening the attachment of the bucket to the turbine wheel. In addition, the lip and shoulder arrangement permits the location of the center of gravity of the bucket blade centrally between legs 8, thereby equalizing stresses in the legs.

Tests have indicated that with the arrangement herein disclosed for mounting buckets on a turbine wheel, the fatigue failure of blades adjacent the bucket base is substantially eliminated. The explanation seems to be that the natural frequency of vibration of the turbine bucket in a tangential direction is changed to the extent that the impulses imparted to the blades by the discrete jets issuing from the turbine nozzles at normal operating speeds no longer build up vibrations that rupture the bucket. It will be appreciated by those skilled in the art that an axial flow turbine bucket tends to vibrate both in an axial plane and tangentially in the plane of the wheel, the latter tan- 3 gential vibration being most conducive to fatigue failures.

In assembling a turbine wheel according to the above principles, turbine buckets l are axially inserted over lands 9 that are provided at the outer periphery, ofthe turbine wheel. The buckets are consecutively driven over lands 9; alternate legs 8 of two consecutive turbine buckets substantially fill one V-groove 2 cut in the periphery of the turbine wheel. The buckets are installed around the periphery of the turbine wheel, after which a shroud ring (not shown) of a conventional type may be added to completely surround the outer ends of the blades to strengthen them.

While the invention has been described as applied to a turbine bucket wheel, it will be apparent that it may also be used in connecting blades to the discs of an axial flow compressor. Modifications of this invention will occur to those skilled in the art and it isdesired to be understood, therefore, that this invention is not to be limited to the particular arrangement disclosed. but that the appended claim is meant to cover all the modifications which are within the spirit and scope of this invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

A bladed turbo-machine wheel having circumferentially spaced axially extending V-shaped grooves in the periphery thereof, each provided with serrations in both walls of the groove and substantially parallel to the axis of the wheel, a plurality of buckets, each comprising a blade secured to a base portion with an axially extending inverted V-shaped groove formed centrally therein to define a pair of circumferentially spaced legs, each leg having an exterior side REFERENCES CITED The following references are of record in the file'of this patent:

I UNITED STATES PATENTS Number Name Date 1,720,729 Hanzlik July 16, 1929 2,271,971 Doran Feb. 3, 1942 FOREIGN PATENTS Number Country Date Germany Mar. 18, 1921 

